Internal teeth oscillating inner gearing planetary gear system

ABSTRACT

An internal teeth oscillating inner gearing planetary gear system is provided with an input shaft, an eccentric gear rotated by the input shaft, the internal oscillating body oscillatingly rotated through the inner circumferential surface of the eccentric gear, and an external gear meshed with the internal oscillating body.

This application is a Divisional of U.S. patent application Ser. No.10/803,102, filed Mar. 18, 2004. The disclosure of the prior applicationis hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an internal teeth oscillating innergearing planetary gear system.

2. Description of the Related Art

In the art, inner gearing planetary gear systems are employed widely invarious reducer fields owing to the advantages of large torquetransmission as well as the ability to achieve large reduction ratios.

Among reducers, internal teeth oscillating inner gearing planetary gearsystems are known wherein the rotation of an input shaft is reduced inspeed and delivered from an output member by oscillatingly rotatinginternal oscillating bodies around an external gear, the internaloscillating body having a slight difference in the number of teeth withthe external gear (for example, Japanese Patent No. 2607937).

An example of the same gear system will be explained with reference toFIGS. 3 and 4.

In the drawings, a casing 1 has a first support block 1A and a secondsupport block 1B joined together by insertion of an engaging member suchas a bolt or pin (omitted in drawings) into engaging holes 2. A pinion 6is disposed on the end of an input shaft 5. The pinion 6 meshes with aplurality of transmitting gears 7 disposed at equal angles around theinput shaft 5.

Three eccentric shafts 10 are disposed in the casing 1 at equal-angledintervals (120 degree intervals) circumferentially. The eccentric shafts10 are supported in a freely rotatable manner by bearings 8 and 9 atboth axial ends and have eccentric bodies 10A and 10B in an axiallymidway portion. The transmitting gears 7 are joined to respective endportions of the eccentric shafts 10. The transmitting gears 7 arerotated by the rotation of the input shaft 5, to rotate each of theeccentric shafts 10.

The eccentric shafts 10 pass through eccentric holes 11A and 11B of twointernal oscillating bodies 12A and 12B contained in the casing 1,respectively. Rollers 14A and 14B are disposed between outercircumferences of the two eccentric bodies 10A and 10B adjoined in theaxial direction of the eccentric shafts 10 and inner circumferences ofthe through eccentric holes 11A and 11B of the internal oscillatingbodies 12A and 12B, respectively.

An external gear 21 integrated with the end of an output shaft 20 isdisposed at the central portion inside the casing 1. Internal teeth 13formed from pins of the internal oscillating bodies 12A and 12B meshwith external teeth 23 of the external gear 21. A difference in thenumber of teeth between the external teeth 23 of the external gear 21and the internal teeth 13 of the internal oscillating bodies 12A and 12Bis set to be slight (for example, in a range of about 1 to 4).

The gear system operates in the following manner.

Rotation of the input shaft 5 is delivered to the transmitting gears 7through the pinion 6. The eccentric shafts 10 are then rotated by thetransmitting gears 7. The eccentric bodies 10A and 10B rotate due torotation of the eccentric shafts 10, then the internal oscillatingbodies 12A and 12B oscillatingly rotate due to the rotation of theeccentric bodies 10A and 10B. With this arrangement, through onerotation of the oscillating rotation of the internal oscillating bodies12A and 12B, a phase of the external gear 21 which meshes with theinternal oscillating bodies 12A and 12B is shifted by the difference inthe number of teeth. Thus, a rotation component equivalent to the phasedifference becomes the (reduction) rotation of the external gear 21, andoutput of reduced speed is delivered from the output shaft 20.

However, according to this known gear system, since the internaloscillating bodies 12A and 12B are oscillatingly rotated by the threeeccentric shafts 10, elements such as the transmitting gears 7 and therollers 14 must be provided corresponding to the number of the eccentricshafts 10. The number of components is therefore large, and as a resultit is difficult to realize cost reduction.

Also, since the single (pinion 6 of the) input shaft 5 rotates the threetransmitting gears 7 which are disposed circumferentially at equalintervals, the input shaft 5 must be located in the central portion ofthe gear system. Thus, for example, it is difficult to form athrough-hole in the central portion of a gear system to pass wiring,piping, etc. therethrough.

Moreover, since a single internal oscillating body 12A (12B) is drivenby three eccentric shafts 10, it is necessary to fabricate and assembleeach member with high accuracy in order to rotate the internaloscillating body 12A (12B) smoothly in a balanced manner.

SUMMARY OF THE INVENTION

The present invention was devised to solve these problems. It is anobject to provide an internal teeth oscillating inner gearing planetarygear system in which layout space for piping, wiring, etc. can be easilymaintained in the central portion of the system corresponding toparticular applications, and in which further smoothness of powertransmission can be achieved, while cost reduction by reducing thenumber of components, reduction of burden of stock, and other effectsare made possible.

The present invention provides an internal teeth oscillating innergearing planetary gear system in which the rotation of an input shaft isreduced in speed and delivered from an output member by oscillatinglyrotating an internal oscillating body around an external gear. Theinternal oscillating body has a slight difference in the number of teethwith the external gear. An eccentric gear rotated by the input shaft hasan eccentric inner circumferential surface with respect to itsrotational center. The eccentric gear is disposed radially outward ofthe internal oscillating body. The internal oscillating body isoscillatingly rotated via the inner circumferential surface of theeccentric gear. Thus, the aforementioned problem is solved.

According to the present invention, internal oscillating bodies, whichhad been oscillatingly rotated by a plurality of eccentric shaftsformerly, are oscillatingly rotated by one eccentric gear. Therefore,there is no need to dispose several sliding members such as rollers,transmitting gears, etc., which had to be disposed for each of severaleccentric shafts. Thus, the cost is reduced through decreasing thenumber of components. Particularly, when several capacities,transmission ratios, etc. are to be provided as a group of gear systems,the entire number of stock components can be largely reduced. Moreover,an internal oscillating body can be driven by a single eccentric gear,so that the internal oscillating body can be oscillatingly rotatedsmoothly in a balanced manner. Thus a further smoothness of powertransmission will be possible.

Further, since an eccentric gear is located radially outside theinternal oscillating body, an input shaft for driving the eccentric geardoes not have to be located in a central portion of a gear system.Accordingly, there is a greater degree of freedom in locating an inputshaft. The space in the central portion of the gear system can also beused effectively.

Therefore, the input shaft may be placed radially outside the eccentricgear, for example, in a case where a gear for meshing with a piniondisposed on the input shaft is disposed at an outer circumferentialportion of the eccentric gear. With this arrangement, through-space forpiping, wiring, etc. can then be easily provided in the central portionof the gear system. Therefore, various examples of the present inventionare particularly beneficial in applications such as joint drives inindustrial robots. Also, if needed, a desired reduction ratio can beobtained while using the same internal oscillating body and othercomponents by changing the pinion of the input shaft and the gear of theeccentric gear. By changing the pinion diameter and/or the geardiameter, the offset amount of the input shaft with respect torotational axis of an output-end member (partnered apparatus) can alsobe optimally designed in response to usage applications, installationlocation, and other considerations.

Further, if a plurality of the internal oscillating bodies are providedin the axial direction for the same eccentric gear, the plurality ofinternal oscillating bodies can be simultaneously oscillatingly rotatedby the single eccentric gear, and the amount of power transmission canbe increased.

Moreover, if the input shaft is placed parallel to the axis of theeccentric gear, and the pinion of the input shaft is placed on anextension in the radial direction of the internal oscillating body, thewidth dimension of the gear system when viewing the input shaft from theside can be made smaller. Thus, the gear system can be designed smaller.

A construction may also be adopted wherein the input shaft is placed ata right angle to the axis of the eccentric gear, and an orthogonal gearmechanism is formed by the pinion of the input shaft and the gear of theeccentric gear. In this instance, a drive device for driving the gearsystem can be located in the radial direction of the gear system, toprovide compactness of space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a lateral cross-sectional view of an internal teethoscillating inner gearing planetary gear system according to anembodiment of the present invention;

FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1;

FIG. 3 is a lateral cross-sectional view of an internal teethoscillating inner gearing planetary gear system of the related art; and

FIG. 4 is a cross-sectional view taken along the line VI-VI in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the drawings, an embodiment of the present inventionwill be described.

FIGS. 1 and 2 are drawings showing an internal teeth oscillating innergearing planetary gear system 100 (hereafter, simply gear system)according to an embodiment of the present invention. FIG. 1 is a lateralcross-sectional view of the gear system 100, and FIG. 2 is across-sectional view taken along the line II-II in FIG. 1.

As shown in the drawings, the gear system 100 mainly comprises a mainbody casing 102, an input shaft 104, an eccentric gear 106, two internaloscillating bodies 108A and 108B, and an external gear 110 also servinga function as an output shaft.

The main body casing 102 comprises a first casing 102A and a secondcasing 102B located at the left and right respectively in FIG. 1. Aplurality of bolt holes 102A1 and 102B1 are formed respectively in thefirst casing 102A and the second casing 102B so as to pass therethrough.The first casing 102A and the second casing 102B are mutually joinableby bolts (not shown).

The input shaft 104 is placed sideways in the main body casing 102 inFIG. 1. An end 104A (left of drawing) of the input shaft 104 isrotatably supported by a first bearing 112 disposed in the first casing102A. Near the center of the input shaft 104, an input shaft cover 113is attached to the second casing 102B by bolts 111, and the input shaft104 is rotatably supported in the center vicinity thereof by a secondbearing 114 disposed in the input shaft cover 113. Further, another end104B (right of drawing) of the input shaft 104 extends to projectoutside the input shaft cover 113, and is connectable with a drivedevice (not shown) such as a motor. Further, a pinion 104C with asomewhat larger diameter than the axial diameter of the input shaft 104is disposed at an outer circumferential portion of the input shaft 104between the first bearing 112 and the second bearing 114, and the inputshaft 104 meshes with the eccentric gear 106 through the pinion 104C.

The eccentric gear 106 is made up of a substantially ring-shaped memberlocated radially outside the input shaft 104, and is supported to berotatable by a third bearing 116 disposed in the first casing 102A andby a fourth bearing 118 disposed in the second casing 102B. A gear 106Cis formed at an outer circumferential portion of the eccentric gear 106,and is meshable with the pinion 104C of the input shaft 104.

As shown in FIG. 2, a first inner circumferential surface 106A processedto be eccentric by an amount E1 with respect to a rotational center L1of the eccentric gear 106, and a second inner circumferential surface106B (shown only in FIG. 1) processed to be eccentric with a 180 degreephase difference relative to the first inner circumferential surface106A, are formed at an inner circumferential portion of the eccentricgear 106. The two internal oscillating bodies 108A and 108B arerespectively located further inside the inner circumference of the innercircumferential surfaces 106A and 106B through rollers 120A and 120B.

The internal oscillating bodies 108A and 108B are made up ofsubstantially ring-shaped members having somewhat smaller diameters thanthe eccentric gear 106, and a plurality of internal teeth 108A1 and108B1 having a trochoid tooth profile are formed on inner circumferencesthereof. Further, the previously discussed pinion 104C of the inputshaft 104 is located to be on an extension in the radial direction ofthe internal oscillating bodies 108A and 108B. “Located to be on anextension in the radial direction” here means that an axial positioningof the internal oscillating bodies 108A and 108B and an axialpositioning of the pinion 104C are mutually overlapped at leastpartially in the radial direction. Further, the external gear 110 whichmeshes with the internal oscillating bodies 108A and 108B is locatedfurther inside the inner circumference of the internal oscillatingbodies 108A and 108B.

The external gear 110 is made up of a substantially tubular memberhaving a through-hole 110A through which piping, wiring, etc. can pass.A portion of the outer circumference of the external gear 110 isstructured such that external pins 110C are fitted to be freelyrotatable in plurally formed circular grooves 110B. The plurality ofexternal pins 110C form external teeth of the external gear 110 meshablewith the internal teeth 108A1 and 108B1 of the internal oscillatingbodies 108A and 108B. Further, the external gear 110 is rotatablysupported by two bearings 120 and 122 disposed inside the first casing102A and the second casing 102B respectively. The bearings 120 and 122are kept from moving axially by flanges 128 and 130 secured by bolts 124and 126 at both ends. Finally, an output-end member (partneredapparatus) (not shown) is joined through bolt holes 132 formed in theflange 130, so that rotational output of the external gear 110 isdelivered to outside.

Next, operation of the gear system 100 according to the embodiment ofthe present invention will be described.

Rotation inputted to the input shaft 104 is transmitted to the eccentricgear 106 through the pinion 104C of the input shaft 104 and the gear106C of the eccentric gear 106 which meshes therewith. Upon rotation ofthe eccentric gear 106, the two internal oscillating bodies 108A and108B are guided by the inner circumferential surfaces 106A and 106Brespectively of the eccentric gear 106, and are oscillatingly rotated.Owing to this arrangement, through one oscillating rotation of theinternal oscillating bodies 108A and 108B, the external gear 110 meshingwith the internal oscillating bodies 108A and 108B becomes out of phaseaccording to the difference in the number of teeth thereof. A rotationalcomponent equivalent to the phase difference thereof thus makes therotation of the external gear 110, and output is delivered to outside.

According to the gear system 100 in accordance with the presentembodiment of the invention, the internal oscillating bodies 108A and108B, which had been oscillatingly rotated conventionally by a pluralityof eccentric shafts, can be oscillatingly rotated by the singleeccentric gear 106. Therefore, it is unnecessary to provide a pluralityof sliding members such as rollers, transmitting gears, etc. which hadto be provided for each of a plurality of eccentric shafts. Costreductoin is then enabled owing to a reduction in the number ofcomponents. Particularly when a plurality of capacities, transmissionratios, etc. are to be provided as a product group for the gear systems100, the total number of stock components can be largely reduced. Inaddition, the internal oscillating bodies 108A (108B) can beoscillatingly rotated in a smooth and balanced manner and furthersmoothness of power transmission can be achieved by driving the internaloscillating bodies 108A (108B) by the single eccentric gear 106.

Also, since the eccentric gear 106 is located radially outside theinternal oscillating bodies 108A and 108B, the input shaft 104 fordriving the eccentric gear 106 does not necessarily have to be locatedin the center portion of the gear system 100. Therefore, the degree offreedom in locating the input shaft 104 is increased so that a space inthe center portion of the gear system 100 can be used effectively.

Specifically, since the gear 106C is disposed at the outercircumferential portion of the eccentric gear 106 to mesh with thepinion 104C disposed on the input shaft 104 and the input shaft 104 islocated radially outside the eccentric gear 106, the through-hole 110Athrough which piping, wiring, etc. pass can be provided in the externalgear 110 located at the central portion of the gear system 100.Therefore, the present invention is particularly useful in applicationssuch as joint drive in industrial robots, for example. Further, bychanging the pinion 104C of the input shaft 104 and the gear 106C of theeccentric gear 106, a desired reduction ratio can be achieved whileusing the same internal oscillating bodies 108A and 108B and otherstructural elements. Also, by varying the radial dimensions of thepinion 104C, the gear 106C, etc., the amount of offset of the inputshaft 104 with respect to the rotational center of an output-end member(mating apparatus) can be optimally designed according to intendedusage, location of installation, and other factors. Further, since theinput shaft 104 is located parallel to the axis L1 of the eccentric gear106, and since the pinion 104C of the input shaft 104 is located to beon an extension in the radial direction of the internal oscillatingbodies 108A and 108B, the width dimension (axial dimension) of the gearsystem 100 when viewing the input shaft 104 from the side can be madesmaller, and a more compact design of the gear system 100 can beprovided.

Further, since the two internal oscillating bodies 108A and 108B areprovided for the same eccentric gear 106, the plurality of internaloscillating bodies 108A and 108B can be oscillatingly rotatedsimultaneously by the single eccentric gear 106. An increase in theamount of power to be transmitted can thus be achieved. Further, thepresent invention is not limited in this manner, and may be a gearsystem comprising only one internal oscillating body, or may be a gearsystem comprising three or more.

Also according to the aforementioned embodiment, the internal teeth108A1 and 108B1 of the internal oscillating bodies 108A and 108B havetrochoid tooth profiles, and the external teeth 110C of the externalgear 110 have a circular tooth profile, however, the present inventionis not limited in this manner. For example, the internal teeth of theinternal oscillating bodies may have circular tooth profiles while theexternal teeth of the external gear have a trochoid tooth profile, orboth may have involute tooth profiles, etc.

Further, according to the aforementioned embodiment, the input shaft 104is located parallel to the axis L1 of the eccentric gear 106, however,the present invention is not limited in this manner. The input shaft maybe located at a right angle to the axis of the eccentric gear, yieldinga structure wherein an orthogonal gear mechanism (hypoid gears, bevelgears) is formed by the pinion of the input shaft and the gear of theeccentric gear. With such an arrangement, a drive device such as a motorfor driving the gear system can be located radially relative to the gearsystem, and less space can be occupied.

According to the present invention, an internal teeth oscillating innergearing planetary gear system can be provided which can easily maintainlayout space for piping, wiring, etc. in the central portion of thesystem according to particular applications, and which can achievefurther smoothness of power transmission, while cost reduction throughreduction of the number of components, reduction of stock burden, andother effects can be realized.

The disclosure of Japanese Patent Application No. 2003-75296 filed Mar.19, 2003 including specification, drawings and claims is incorporatedherein by reference in its entirety.

1. An internal teeth oscillating inner gearing planetary gear systemcomprising: an input shaft; an eccentric gear being rotated by the inputshaft and having an eccentric inner circumferential surface with respectto a rotational center thereof; an internal oscillating body beingguided by the inner circumferential surface of the eccentric gear andoscillatingly moved thereby, the internal oscillating body havinginternal teeth on an inner periphery thereof; an external gearinternally meshing with the internal oscillating body, the external gearhaving slightly less number of external teeth than that of the internalteeth of the internal oscillating body.
 2. The internal teethoscillating inner gearing planetary gear system according to claim 1,wherein a gear for meshing with a pinion disposed on the input shaft isdisposed at an outer circumferential portion of the eccentric gear, andthe input shaft is placed radially outside the eccentric gear.
 3. Theinternal teeth oscillating inner gearing planetary gear system accordingto claim 2, wherein the input shaft is placed parallel to an axis of theeccentric gear, and the pinion of the input shaft is placed to be on anextension in the radial direction of the internal oscillating body. 4.The internal teeth oscillating inner gearing planetary gear systemaccording to claim 2, wherein the input shaft is placed at a right angleto an axis of the eccentric gear, and an orthogonal gear mechanism isformed by the pinion of the input shaft and the gear of the eccentricgear.
 5. A driving method of an inner teeth gearing planetary gearsystem, the system having an input shaft, an output shaft, an externalgear, and an internal oscillating body, the method comprising the stepsof: transmitting rotation of the input shaft to an eccentric gear, theeccentric gear having an eccentric inner circumferential surface withrespect to a rotational center thereof; oscillatingly rotating theinternal oscillating body by using the inner circumferential surface ofthe eccentric gear as a guide surface, the internal oscillating bodyhaving internal teeth on an inner periphery thereof and meshing with theexternal gear through the internal teeth; and restricting any one ofrotations of the internal oscillating body and the external gear, anddelivering a rotational component of the other whose rotation is notrestricted for output.